Material Control Data object with different PG than owner part.
The material control data and its associate part occurrence have different permission groups.
For on-the-fly items, the catalog part or the material control data object are copied into the model with different parent groups.
If you are working with a parent permission group that does not have access to the child support object, you may not be able to modify the child.
What You Should Do
Open the model.
Run the Clean Database custom command.
Select the target objects, and then click Clean Now.